Design And Development Of New Metacarpophalangeal Joint Prosthesis

Objectives:1.To provide anatomical basis for the shape and size of artificial metacarpophalangeal joint prosthesis,by studying the anatomy of the metacarpophalangeal joint,measurement of medullary cavity data of metacarpal and proximal phalanx,measurement of articular surface curvature and arc length and other data.2.To design and manufacture a new type of metacarpophalangeal joint prosthesis based on the experiment study and applied primarily.Methods:1.First,thirteen adult fresh frozen hands were dissected to preserve the metacarpophalangeal joint and its surrounding structure,to observe the structure of maintaining the stability of the metacarpophalangeal joint,and to measure the relevant data of the joint and the bone medullary cavity of metacarpal bone and proximal finger.Secondly,the imaging data of 10 adults who underwent hand CT scanning in 920 Hospital of Chinese PLA from 2017 to 2019 were collected.Mimics,3-Matic and other software were used to fit the basal articular surface of metacarpal head and proximal phalanx by digital technology,and the radius of curvature and arc length were measured.All the data were analyzed by SPSS software.2.According to the statistical results of anatomical measurement and the particularity of the shape of the bone marrow cavity of metacarpal and proximal finger,the joint prosthesis material was selected.Considering the shape of metacarpophalangeal joint and the particularity of joint materials,the three-dimensional map of the prosthesis was designed,and then the preliminary processing of the prosthesis was carried out according to the three-dimensional map.3.The metacarpophalangeal joint prosthesis was preliminarily applied to frozen cadaveric hand specimens.Results:1.The stability of each metacarpophalangeal joint is maintained by joint surface shape,joint capsule and collateral ligament2.The articular surface of each metacarpophalangeal varies in size and the sagittal diameter of each metacarpal head is:index finger>middle finger>ring finger>thumb>little finger;the coronal diameter of each metacarpal head is:thumb>index finger>middle finger>ring finger>little finger;the sagittal diameter of each proximal phalanx basal is:middle finger>index finger>thumb>ring finger>little finger;the coronal diameter of each proximal phalanx basal is:thumb>index finger>middle finger>ring finger>little finger;there were significant differences in the basal coronal diameter and sagittal diameter of each metacarpal head and proximal phalanx(P<0.05).3.Except for the particularity of the thumb metacarpophalangeal joint,which is different from the other four fingers,each metacarpophalangeal joint is similar in shape and different in size.The radius of curvature of the synthetic circle in the median sagittal plane of each metacarpal head is:middle finger>index finger>thumb>ring finger>little finger;the arc length of the articular surface of the median sagittal plane of the metacarpal head is:middle finger>index finger>ring finger>thumb>little finger,there are significant differences in the radius of curvature and the arc length of the articular surface in the median sagittal plane of each metacarpal head(P<0.05).The radius of curvature of the synthetic circle in the sagittal plane of the base of the proximal phalanx is as follows:thumb>index finger>ring finger>little finger>middle finger,P>0.05,the arc length of the articular surface is:middle finger>index finger>thumb>ring finger>little finger,P<0.05;it can be considered that the radius of curvature of the base of the proximal phalanx of each finger is similar,but the difference of the arc length of the articular surface is statistically significant.4.According to the results of the data and the shape of the medullary cavity,the joint material is selected as Ni-Ti memory alloy,taking the mean data of the metacarpophalangeal joint of the index finger as an example,the three-dimensional diagram of the prosthesis is designed,the joint prosthesis is made with the three-dimensional picture as the model,which is preliminarily applied to cadaveric hand specimens.Conclusions:1.The design of artificial joint prosthesis should be in accordance with the anatomical characteristics,and joint replacement especially needs to protect the structure that maintains the stability of the joint2.The thumb metacarpophalangeal joint is different from the second to fourth fingers,and the prosthesis should be designed differently;the rest of the metacarpophalangeal joints can be designed with the same shape and different types of prosthesis.3.The shape and size of the bone marrow cavity of the metacarpal bone and the proximal finger are not the same,the memory function of Ni-Ti memory alloy can avoid the limitation of irregular shape of medullary cavity on the design of prosthesis,through memory function and tail barb,it can put pressure on the lateral wall of the medullary cavity and achieve preliminary stability.